workstation-v0 surface aggregate polish warnings in status

[mdheller]

Adds minimal status integration for the aggregate workstation polish validation helper.

Scope:

• consume check-workstation-polish.sh from sourceos status
• append warnings for missing aggregate helper, missing Mac/keyboard helper signals, or invalid keyboard policy
• preserve the existing status JSON schema

Critic notes:

• intentionally does not modify doctor.sh yet
• keeps the change limited to sourceos
• branch is current and one-file scoped